1. Field of the Invention
This invention relates to a wire stripping machine for stripping the insulation from the end of an insulated wire and, more particularly, to a wire stripping machine and element therefor for simultaneously stripping the insulation from the end of a stranded-core, insulated wire and twisting the conductor strands.
2. Prior Art
In the manufacture of stranded-core electrical power cords, for example, two-wire power cords for use with electrically operated devices including power tools and appliances, the power cord is typically manufactured by removing a predetermined length of cord from a supply reel and preparing one or both ends of the cord by removing a portion of the outer insulating jacket, removing the jute filler-strings, unwrapping the helically wrapped wires, removing the insulation from the wires that extend from the outer jacket, and then twisting the exposed conductor strands. The so-prepared wire ends may then be crimped-fitted to an electrical terminal or tinned with solder in preparation for a subsequent soldering operation, for example.
Two general types of stripping machines, the rotating head type and the reciprocating bar type, are known in the prior art for removing insulation from the end of a stranded-core insulated wire and twisting the exposed conductor strands.
The rotating head machine, as disclosed in U.S. Pat. No. 2,783,525 to Scharf and U.S. Pat. No. 3,881,374 to Gudmestead, for example, includes a rotatable head which accepts the end of an insulated wire aligned along a wire stripping axis. The head carries a blade or blades which penetrate the insulation near the end of the wire to a depth less than the insulation wall thickness to prevent nicking or damage to the wire core. The head is then rotated about the wire stripping axis causing the cutting edge or edges to effect a peripheral cut so that the end of the wire has a continuous, encircling cut that extends partially through the insulated wire leaving only a small annular ring of uncut insulation adjacent the wire core. The so-cut wire and the stripping head are then separated from one another, either by pulling the wire from the head or by pulling the head from the wire, causing the insulation to separate at its cut-plane. The stripping head continues to rotate as the insulation is separated to cause the so-separated insulation to twist the conductor strands to provide the finished wire.
The reciprocating bar stripping machines, as disclosed in U.S. Pat. No. 3,994,188 and U.S. Pat. No. 4,009,738, both to Baba et al, can simultaneously strip the insulation from and twist the conductor strands of a plurality of wires. These machines include first and second insulation cutting blades that overlie one another in adjacent plane and are mounted on a support for movement between an open, spaced-apart position and a closed, operative position in which the blades converge on the wires from opposite ends. Each blade carries sharpened V-notches with the blades defining complementary notch sets for each wire to be stripped. When the blades converge on the wires, the cutting edges of each V-notch set cut or score the insulation on each wire in four zones distributed about the periphery of the wire with the cut-plane including both cut and partially cut portions. After the cutting step, first and second bars grip the so-cut end of the wires from opposite sides and are caused to move in opposite lateral directions of the wires as the wires are pulled from the machine. The insulation on each wire is separated at its respective cut-plane and pulled from the wire as it is rotated to twist the conductor strands.
Each of the two general types of stripping machines have various advantages and drawbacks. The rotating head machine, by providing an encircling cut about the entire periphery of the insulated wire, permits the insulation to be separated cleanly in its cut-plane without undue tearing. However, since the stripping head must rotate about a wire axis to provide the encircling cut, the rotating head machines are best suited for stripping insulation from a single wire and have limited efficacy for stripping insulation from a plurality of wires, for example, the two wires extending from the end of an electrical power cord. The reciprocating bar machines, on the other hand, can strip the insulation from a plurality of wires but cannot provide the encircling cut about the periphery of the wires that permits clean separation of the insulation. The cutting edges of the complementary V-notches leaves both cut and partially cut zones about the periphery of the insulation. As a result, the insulation, as it is separated in its cut plane, can tear unevenly and leave an irregular edge. From a practical standpoint, the use of V-notch blades requires each cutting edge to be precisely ground with respect to the other edges and each of the wires to be precisely aligned relative to the other and the various cutting edges. Any misalignment in the manufacture of the blades or in the presentation of the wires to the blades can cause the conductors strands to be cut by the cutting edges.